merge trunk

47 files changed, 1065 insertions, 140 deletions

diff --git a/bin/nova-manage b/bin/nova-manage
index 36c677b38..b0cd343f5 100755
--- a/bin/nova-manage
+++ b/bin/nova-manage
@@ -53,7 +53,6 @@
   CLI interface for nova management.
 """
 
-import datetime
 import gettext
 import glob
 import json
@@ -690,7 +689,7 @@ class ServiceCommands(object):
         """Show a list of all running services. Filter by host & service name.
         args: [host] [service]"""
         ctxt = context.get_admin_context()
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         services = db.service_get_all(ctxt)
         if host:
             services = [s for s in services if s['host'] == host]
@@ -1082,24 +1081,35 @@ class ImageCommands(object):
         self._convert_images(machine_images)
 
 
+class ConfigCommands(object):
+    """Class for exposing the flags defined by flag_file(s)."""
+
+    def __init__(self):
+        pass
+
+    def list(self):
+        print FLAGS.FlagsIntoString()
+
+
 CATEGORIES = [
-    ('user', UserCommands),
     ('account', AccountCommands),
-    ('project', ProjectCommands),
-    ('role', RoleCommands),
-    ('shell', ShellCommands),
-    ('vpn', VpnCommands),
+    ('config', ConfigCommands),
+    ('db', DbCommands),
     ('fixed', FixedIpCommands),
+    ('flavor', InstanceTypeCommands),
     ('floating', FloatingIpCommands),
+    ('instance_type', InstanceTypeCommands),
+    ('image', ImageCommands),
     ('network', NetworkCommands),
-    ('vm', VmCommands),
+    ('project', ProjectCommands),
+    ('role', RoleCommands),
     ('service', ServiceCommands),
-    ('db', DbCommands),
+    ('shell', ShellCommands),
+    ('user', UserCommands),
+    ('version', VersionCommands),
+    ('vm', VmCommands),
     ('volume', VolumeCommands),
-    ('instance_type', InstanceTypeCommands),
-    ('image', ImageCommands),
-    ('flavor', InstanceTypeCommands),
-    ('version', VersionCommands)]
+    ('vpn', VpnCommands)]
 
 
 def lazy_match(name, key_value_tuples):
diff --git a/doc/source/devref/distributed_scheduler.rst b/doc/source/devref/distributed_scheduler.rst
new file mode 100644
index 000000000..eb6a1a03e
--- /dev/null
+++ b/doc/source/devref/distributed_scheduler.rst
@@ -0,0 +1,168 @@
+..
+      Copyright 2011 OpenStack LLC 
+      All Rights Reserved.
+
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+Distributed Scheduler
+=====
+
+The Scheduler is akin to a Dating Service. Requests for the creation of new instances come in and the most applicable Compute nodes are selected from a large pool of potential candidates. In a small deployment we may be happy with the currently available Change Scheduler which randomly selects a Host from the available pool. Or if you need something a little more fancy you may want to use the Availability Zone Scheduler, which selects Compute hosts from a logical partitioning of available hosts (within a single Zone). 
+
+But for larger deployments a more complex scheduling algorithm is required. Additionally, if you are using Zones in your Nova setup, you'll need a scheduler that understand how to pass instance requests from Zone to Zone.
+
+This is the purpose of the Distributed Scheduler (DS). The DS utilizes the Capabilities of a Zone and its component services to make informed decisions on where a new instance should be created. When making this decision it consults not only all the Compute nodes in the current Zone, but the Compute nodes in each Child Zone. This continues recursively until the ideal host is found.
+
+So, how does this all work?
+
+This document will explain the strategy employed by the `ZoneAwareScheduler` and its derivations. You should read the Zones documentation before reading this.
+
+Costs & Weights
+----------
+When deciding where to place an Instance, we compare a Weighted Cost for each Host. The Weighting, currently, is just the sum of each Cost. Costs are nothing more than integers from `0 - max_int`. Costs are computed by looking at the various Capabilities of the Host relative to the specs of the Instance being asked for. Trying to putting a plain vanilla instance on a high performance host should have a very high cost. But putting a vanilla instance on a vanilla Host should have a low cost. 
+
+Some Costs are more esoteric. Consider a rule that says we should prefer Hosts that don't already have an instance on it that is owned by the user requesting it (to mitigate against machine failures). Here we have to look at all the other Instances on the host to compute our cost. 
+
+An example of some other costs might include selecting:
+* a GPU-based host over a standard CPU
+* a host with fast ethernet over a 10mbps line
+* a host that can run Windows instances
+* a host in the EU vs North America
+* etc
+
+This Weight is computed for each Instance requested. If the customer asked for 1000 instances, the consumed resources on each Host are "virtually" depleted so the Cost can change accordingly. 
+
+nova.scheduler.zone_aware_scheduler.ZoneAwareScheduler
+-----------
+As we explained in the Zones documentation, each Scheduler has a `ZoneManager` object that collects "Capabilities" about child Zones and each of the services running in the current Zone. The `ZoneAwareScheduler` uses this information to make its decisions.
+
+Here is how it works:
+
+1. The compute nodes are filtered and the nodes remaining are weighed.
+1a. Filtering the hosts is a simple matter of ensuring the compute node has ample resources (CPU, RAM, Disk, etc) to fulfil the request. 
+1b. Weighing of the remaining compute nodes assigns a number based on their suitability for the request.
+2. The same request is sent to each child Zone and step #1 is done there too. The resulting weighted list is returned to the parent.
+3. The parent Zone sorts and aggregates all the weights and a final build plan is constructed.
+4. The build plan is executed upon. Concurrently, instance create requests are sent to each of the selected hosts, be they local or in a child zone. Child Zones may forward the requests to their child Zones as needed.
+
+`ZoneAwareScheduler` by itself is not capable of handling all the provisioning itself. Derived classes are used to select which host filtering and weighing strategy will be used.
+
+Filtering and Weighing
+------------
+The filtering (excluding compute nodes incapable of fulfilling the request) and weighing (computing the relative "fitness" of a compute node to fulfill the request) rules used are very subjective operations ... Service Providers will probably have a very different set of filtering and weighing rules than private cloud administrators. The filtering and weighing aspects of the `ZoneAwareScheduler` are flexible and extensible.
+
+Requesting a new instance
+------------
+Prior to the `ZoneAwareScheduler`, to request a new instance, a call was made to `nova.compute.api.create()`. The type of instance created depended on the value of the `InstanceType` record being passed in. The `InstanceType` determined the amount of disk, CPU, RAM and network required for the instance. Administrators can add new `InstanceType` records to suit their needs. For more complicated instance requests we need to go beyond the default fields in the `InstanceType` table.
+
+`nova.compute.api.create()` performed the following actions:
+1. it validated all the fields passed into it.
+2. it created an entry in the `Instance` table for each instance requested
+3. it put one `run_instance` message in the scheduler queue for each instance requested
+4. the schedulers picked off the messages and decided which compute node should handle the request.
+5. the `run_instance` message was forwarded to the compute node for processing and the instance is created. 
+6. it returned a list of dicts representing each of the `Instance` records (even if the instance has not been activated yet). At least the `instance_id`s are valid. 
+
+Generally, the standard schedulers (like `ChanceScheduler` and `AvailabilityZoneScheduler`) only operate in the current Zone. They have no concept of child Zones.
+
+The problem with this approach is each request is scattered amongst each of the schedulers. If we are asking for 1000 instances, each scheduler gets the requests one-at-a-time. There is no possability of optimizing the requests to take into account all 1000 instances as a group. We call this Single-Shot vs. All-at-Once. 
+
+For the `ZoneAwareScheduler` we need to use the All-at-Once approach. We need to consider all the hosts across all the Zones before deciding where they should reside. In order to handle this we have a new method `nova.compute.api.create_all_at_once()`. This method does things a little differently:
+1. it validates all the fields passed into it.
+2. it creates a single `reservation_id` for all of instances created. This is a UUID.
+3. it creates a single `run_instance` request in the scheduler queue
+4. a scheduler picks the message off the queue and works on it.
+5. the scheduler sends off an OS API `POST /zones/select` command to each child Zone. The `BODY` payload of the call contains the `request_spec`.
+6. the child Zones use the `request_spec` to compute a weighted list for each instance requested. No attempt to actually create an instance is done at this point. We're only estimating the suitability of the Zones.
+7. if the child Zone has its own child Zones, the `/zones/select` call will be sent down to them as well.
+8. Finally, when all the estimates have bubbled back to the Zone that initiated the call, all the results are merged, sorted and processed.
+9. Now the instances can be created. The initiating Zone either forwards the `run_instance` message to the local Compute node to do the work, or it issues a `POST /servers` call to the relevant child Zone. The parameters to the child Zone call are the same as what was passed in by the user.
+10. The `reservation_id` is passed back to the caller. Later we explain how the user can check on the status of the command with this `reservation_id`.
+
+The Catch
+-------------
+This all seems pretty straightforward but, like most things, there's a catch. Zones are expected to operate in complete isolation from each other. Each Zone has its own AMQP service, database and set of Nova services. But, for security reasons Zones should never leak information about the architectural layout internally. That means Zones cannot leak information about hostnames or service IP addresses outside of its world.
+
+When `POST /zones/select` is called to estimate which compute node to use, time passes until the `POST /servers` call is issued. If we only passed the weight back from the `select` we would have to re-compute the appropriate compute node for the create command ... and we could end up with a different host. Somehow we need to remember the results of our computations and pass them outside of the Zone. Now, we could store this information in the local database and return a reference to it, but remember that the vast majority of weights are going be ignored. Storing them in the database would result in a flood of disk access and then we have to clean up all these entries periodically. Recall that there are going to be many many `select` calls issued to child Zones asking for estimates. 
+
+Instead, we take a rather innovative approach to the problem. We encrypt all the child zone internal details and pass them back the to parent Zone. If the parent zone decides to use a child Zone for the instance it simply passes the encrypted data back to the child during the `POST /servers` call as an extra parameter. The child Zone can then decrypt the hint and go directly to the Compute node previously selected. If the estimate isn't used, it is simply discarded by the parent. It's for this reason that it is so important that each Zone defines a unique encryption key via `--build_plan_encryption_key`
+
+In the case of nested child Zones, each Zone re-encrypts the weighted list results and passes those values to the parent.
+
+Throughout the `nova.api.openstack.servers`, `nova.api.openstack.zones`, `nova.compute.api.create*` and `nova.scheduler.zone_aware_scheduler` code you'll see references to `blob` and `child_blob`. These are the encrypted hints about which Compute node to use.
+
+Reservation IDs
+---------------
+
+NOTE: The features described in this section are related to the up-coming 'merge-4' branch. 
+
+The OpenStack API allows a user to list all the instances they own via the `GET /servers/` command or the details on a particular instance via `GET /servers/###`. This mechanism is usually sufficient since OS API only allows for creating one instance at a time, unlike the EC2 API which allows you to specify a quantity of instances to be created.
+
+NOTE: currently the `GET /servers` command is not Zone-aware since all operations done in child Zones are done via a single administrative account. Therefore, asking a child Zone to `GET /servers` would return all the active instances ... and that would be what the user intended. Later, when the Keystone Auth system is integrated with Nova, this functionality will be enabled. 
+
+We could use the OS API 1.1 Extensions mechanism to accept a `num_instances` parameter, but this would result in a different return code. Instead of getting back an `Instance` record, we would be getting back a `reservation_id`. So, instead, we've implemented a new command `POST /zones/boot` command which is nearly identical to `POST /servers` except that it takes a `num_instances` parameter and returns a `reservation_id`. Perhaps in OS API 2.x we can unify these approaches. 
+
+Finally, we need to give the user a way to get information on each of the instances created under this `reservation_id`. Fortunately, this is still possible with the existing `GET /servers` command, so long as we add a new optional `reservation_id` parameter. 
+
+`python-novaclient` will be extended to support both of these changes.
+
+Host Filter
+--------------
+
+As we mentioned earlier, filtering hosts is a very deployment-specific process. Service Providers may have a different set of criteria for filtering Compute nodes than a University. To faciliate this the `nova.scheduler.host_filter` module supports a variety of filtering strategies as well as an easy means for plugging in your own algorithms.
+
+The filter used is determined by the `--default_host_filter` flag, which points to a Python Class. By default this flag is set to `nova.scheduler.host_filter.AllHostsFilter` which simply returns all available hosts. But there are others:
+
+ * `nova.scheduler.host_filter.InstanceTypeFilter` provides host filtering based on the memory and disk size specified in the `InstanceType` record passed into `run_instance`. 
+
+ * `nova.scheduler.host_filter.JSONFilter` filters hosts based on simple JSON expression grammar. Using a LISP-like JSON structure the caller can request instances based on criteria well beyond what `InstanceType` specifies. See `nova.tests.test_host_filter` for examples.
+
+To create your own `HostFilter` the user simply has to derive from `nova.scheduler.host_filter.HostFilter` and implement two methods: `instance_type_to_filter` and `filter_hosts`. Since Nova is currently dependent on the `InstanceType` structure, the `instance_type_to_filter` method should take an `InstanceType` and turn it into an internal data structure usable by your filter. This is for backward compatibility with existing OpenStack and EC2 API calls. If you decide to create your own call for creating instances not based on `Flavors` or `InstanceTypes` you can ignore this method. The real work is done in `filter_hosts` which must return a list of host tuples for each appropriate host. The set of all available hosts is in the `ZoneManager` object passed into the call as well as the filter query. The host tuple contains (`<hostname>`, `<additional data>`) where `<additional data>` is whatever you want it to be.
+     
+Cost Scheduler Weighing
+--------------
+Every `ZoneAwareScheduler` derivation must also override the `weigh_hosts` method. This takes the list of filtered hosts (generated by the `filter_hosts` method) and returns a list of weight dicts. The weight dicts must contain two keys: `weight` and `hostname` where `weight` is simply an integer (lower is better) and `hostname` is the name of the host. The list does not need to be sorted, this will be done by the `ZoneAwareScheduler` base class when all the results have been assembled. 
+
+Simple Zone Aware Scheduling
+--------------
+The easiest way to get started with the `ZoneAwareScheduler` is to use the `nova.scheduler.host_filter.HostFilterScheduler`. This scheduler uses the default Host Filter as and the `weight_hosts` method simply returns a weight of 1 for all hosts. But, from this, you can see calls being routed from Zone to Zone and follow the flow of things. 
+
+The `--scheduler_driver` flag is how you specify the scheduler class name.
+
+Flags
+--------------
+
+All this Zone and Distributed Scheduler stuff can seem a little daunting to configure, but it's actually not too bad. Here are some of the main flags you should set in your `nova.conf` file:
+
+::
+  --allow_admin_api=true
+  --enable_zone_routing=true
+  --zone_name=zone1
+  --build_plan_encryption_key=c286696d887c9aa0611bbb3e2025a45b
+  --scheduler_driver=nova.scheduler.host_filter.HostFilterScheduler
+  --default_host_filter=nova.scheduler.host_filter.AllHostsFilter
+
+`--allow_admin_api` must be set for OS API to enable the new `/zones/*` commands.
+`--enable_zone_routing` must be set for OS API commands such as `create()`, `pause()` and `delete()` to get routed from Zone to Zone when looking for instances. 
+`--zone_name` is only required in child Zones. The default Zone name is `nova`, but you may want to name your child Zones something useful. Duplicate Zone names are not an issue.
+`build_plan_encryption_key` is the SHA-256 key for encrypting/decrypting the Host information when it leaves a Zone. Be sure to change this key for each Zone you create. Do not duplicate keys.
+`scheduler_driver` is the real workhorse of the operation. For Distributed Scheduler, you need to specify a class derived from `nova.scheduler.zone_aware_scheduler.ZoneAwareScheduler`.
+`default_host_filter` is the host filter to be used for filtering candidate Compute nodes. 
+
+Some optional flags which are handy for debugging are:
+
+::
+  --connection_type=fake
+  --verbose
+
+Using the `Fake` virtualization driver is handy when you're setting this stuff up so you're not dealing with a million possible issues at once. When things seem to working correctly, switch back to whatever hypervisor your deployment uses.
diff --git a/nova/api/ec2/admin.py b/nova/api/ec2/admin.py
index 4d981f70b..57d0a0339 100644
--- a/nova/api/ec2/admin.py
+++ b/nova/api/ec2/admin.py
@@ -21,7 +21,6 @@ Admin API controller, exposed through http via the api worker.
 """
 
 import base64
-import datetime
 
 from nova import db
 from nova import exception
@@ -305,7 +304,7 @@ class AdminController(object):
             * Volume Count
         """
         services = db.service_get_all(context, False)
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         hosts = []
         rv = []
         for host in [service['host'] for service in services]:
diff --git a/nova/api/ec2/cloud.py b/nova/api/ec2/cloud.py
index ab47843cc..b7a9a8633 100644
--- a/nova/api/ec2/cloud.py
+++ b/nova/api/ec2/cloud.py
@@ -23,7 +23,6 @@ datastore.
 """
 
 import base64
-import datetime
 import IPy
 import os
 import urllib
@@ -235,7 +234,7 @@ class CloudController(object):
                                         'zoneState': 'available'}]}
 
         services = db.service_get_all(context, False)
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         hosts = []
         for host in [service['host'] for service in services]:
             if not host in hosts:
@@ -595,7 +594,7 @@ class CloudController(object):
         instance_id = ec2utils.ec2_id_to_id(ec2_id)
         output = self.compute_api.get_console_output(
                 context, instance_id=instance_id)
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         return {"InstanceId": ec2_id,
                 "Timestamp": now,
                 "output": base64.b64encode(output)}
diff --git a/nova/api/openstack/auth.py b/nova/api/openstack/auth.py
index 6c6ee22a2..b49bf449b 100644
--- a/nova/api/openstack/auth.py
+++ b/nova/api/openstack/auth.py
@@ -13,9 +13,8 @@
 #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
-#    under the License.import datetime
+#    under the License.
 
-import datetime
 import hashlib
 import time
 
@@ -127,7 +126,7 @@ class AuthMiddleware(wsgi.Middleware):
         except exception.NotFound:
             return None
         if token:
-            delta = datetime.datetime.utcnow() - token['created_at']
+            delta = utils.utcnow() - token['created_at']
             if delta.days >= 2:
                 self.db.auth_token_destroy(ctxt, token['token_hash'])
             else:
diff --git a/nova/api/openstack/contrib/__init__.py b/nova/api/openstack/contrib/__init__.py
index b42a1d89d..acb5eb280 100644
--- a/nova/api/openstack/contrib/__init__.py
+++ b/nova/api/openstack/contrib/__init__.py
@@ -13,7 +13,7 @@
 #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
-#    under the License.import datetime
+#    under the License.
 
 """Contrib contains extensions that are shipped with nova.
 
diff --git a/nova/api/openstack/limits.py b/nova/api/openstack/limits.py
index 4d46b92df..dc2bc6bbc 100644
--- a/nova/api/openstack/limits.py
+++ b/nova/api/openstack/limits.py
@@ -11,7 +11,7 @@
 #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
-#    under the License.import datetime
+#    under the License.
 
 """
 Module dedicated functions/classes dealing with rate limiting requests.
diff --git a/nova/api/openstack/ratelimiting/__init__.py b/nova/api/openstack/ratelimiting/__init__.py
index 88ffc3246..9ede548c2 100644
--- a/nova/api/openstack/ratelimiting/__init__.py
+++ b/nova/api/openstack/ratelimiting/__init__.py
@@ -13,7 +13,7 @@
 #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
-#    under the License.import datetime
+#    under the License.
 
 """Rate limiting of arbitrary actions."""
 
diff --git a/nova/auth/ldapdriver.py b/nova/auth/ldapdriver.py
index 3f8432851..183f7a985 100644
--- a/nova/auth/ldapdriver.py
+++ b/nova/auth/ldapdriver.py
@@ -24,6 +24,7 @@ other backends by creating another class that exposes the same
 public methods.
 """
 
+import functools
 import sys
 
 from nova import exception
@@ -68,6 +69,12 @@ flags.DEFINE_string('ldap_developer',
 LOG = logging.getLogger("nova.ldapdriver")
 
 
+if FLAGS.memcached_servers:
+    import memcache
+else:
+    from nova import fakememcache as memcache
+
+
 # TODO(vish): make an abstract base class with the same public methods
 #             to define a set interface for AuthDrivers. I'm delaying
 #             creating this now because I'm expecting an auth refactor
@@ -85,6 +92,7 @@ def _clean(attr):
 
 def sanitize(fn):
     """Decorator to sanitize all args"""
+    @functools.wraps(fn)
     def _wrapped(self, *args, **kwargs):
         args = [_clean(x) for x in args]
         kwargs = dict((k, _clean(v)) for (k, v) in kwargs)
@@ -103,29 +111,56 @@ class LdapDriver(object):
     isadmin_attribute = 'isNovaAdmin'
     project_attribute = 'owner'
     project_objectclass = 'groupOfNames'
+    conn = None
+    mc = None
 
     def __init__(self):
         """Imports the LDAP module"""
         self.ldap = __import__('ldap')
-        self.conn = None
         if FLAGS.ldap_schema_version == 1:
             LdapDriver.project_pattern = '(objectclass=novaProject)'
             LdapDriver.isadmin_attribute = 'isAdmin'
             LdapDriver.project_attribute = 'projectManager'
             LdapDriver.project_objectclass = 'novaProject'
+        self.__cache = None
+        if LdapDriver.conn is None:
+            LdapDriver.conn = self.ldap.initialize(FLAGS.ldap_url)
+            LdapDriver.conn.simple_bind_s(FLAGS.ldap_user_dn,
+                                          FLAGS.ldap_password)
+        if LdapDriver.mc is None:
+            LdapDriver.mc = memcache.Client(FLAGS.memcached_servers, debug=0)
 
     def __enter__(self):
-        """Creates the connection to LDAP"""
-        self.conn = self.ldap.initialize(FLAGS.ldap_url)
-        self.conn.simple_bind_s(FLAGS.ldap_user_dn, FLAGS.ldap_password)
+        # TODO(yorik-sar): Should be per-request cache, not per-driver-request
+        self.__cache = {}
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
-        """Destroys the connection to LDAP"""
-        self.conn.unbind_s()
+        self.__cache = None
         return False
 
+    def __local_cache(key_fmt):
+        """Wrap function to cache it's result in self.__cache.
+        Works only with functions with one fixed argument.
+        """
+        def do_wrap(fn):
+            @functools.wraps(fn)
+            def inner(self, arg, **kwargs):
+                cache_key = key_fmt % (arg,)
+                try:
+                    res = self.__cache[cache_key]
+                    LOG.debug('Local cache hit for %s by key %s' %
+                              (fn.__name__, cache_key))
+                    return res
+                except KeyError:
+                    res = fn(self, arg, **kwargs)
+                    self.__cache[cache_key] = res
+                    return res
+            return inner
+        return do_wrap
+
     @sanitize
+    @__local_cache('uid_user-%s')
     def get_user(self, uid):
         """Retrieve user by id"""
         attr = self.__get_ldap_user(uid)
@@ -134,15 +169,31 @@ class LdapDriver(object):
     @sanitize
     def get_user_from_access_key(self, access):
         """Retrieve user by access key"""
+        cache_key = 'uak_dn_%s' % (access,)
+        user_dn = self.mc.get(cache_key)
+        if user_dn:
+            user = self.__to_user(
+                self.__find_object(user_dn, scope=self.ldap.SCOPE_BASE))
+            if user:
+                if user['access'] == access:
+                    return user
+                else:
+                    self.mc.set(cache_key, None)
         query = '(accessKey=%s)' % access
         dn = FLAGS.ldap_user_subtree
-        return self.__to_user(self.__find_object(dn, query))
+        user_obj = self.__find_object(dn, query)
+        user = self.__to_user(user_obj)
+        if user:
+            self.mc.set(cache_key, user_obj['dn'][0])
+        return user
 
     @sanitize
+    @__local_cache('pid_project-%s')
     def get_project(self, pid):
         """Retrieve project by id"""
-        dn = self.__project_to_dn(pid)
-        attr = self.__find_object(dn, LdapDriver.project_pattern)
+        dn = self.__project_to_dn(pid, search=False)
+        attr = self.__find_object(dn, LdapDriver.project_pattern,
+                                  scope=self.ldap.SCOPE_BASE)
         return self.__to_project(attr)
 
     @sanitize
@@ -395,6 +446,7 @@ class LdapDriver(object):
         """Check if project exists"""
         return self.get_project(project_id) is not None
 
+    @__local_cache('uid_attrs-%s')
     def __get_ldap_user(self, uid):
         """Retrieve LDAP user entry by id"""
         dn = FLAGS.ldap_user_subtree
@@ -426,12 +478,20 @@ class LdapDriver(object):
         if scope is None:
             # One of the flags is 0!
             scope = self.ldap.SCOPE_SUBTREE
+        if query is None:
+            query = "(objectClass=*)"
         try:
             res = self.conn.search_s(dn, scope, query)
         except self.ldap.NO_SUCH_OBJECT:
             return []
         # Just return the attributes
-        return [attributes for dn, attributes in res]
+        # FIXME(yorik-sar): Whole driver should be refactored to
+        #                   prevent this hack
+        res1 = []
+        for dn, attrs in res:
+            attrs['dn'] = [dn]
+            res1.append(attrs)
+        return res1
 
     def __find_role_dns(self, tree):
         """Find dns of role objects in given tree"""
@@ -564,6 +624,7 @@ class LdapDriver(object):
             'description': attr.get('description', [None])[0],
             'member_ids': [self.__dn_to_uid(x) for x in member_dns]}
 
+    @__local_cache('uid_dn-%s')
     def __uid_to_dn(self, uid, search=True):
         """Convert uid to dn"""
         # By default return a generated DN
@@ -576,6 +637,7 @@ class LdapDriver(object):
                 userdn = user[0]
         return userdn
 
+    @__local_cache('pid_dn-%s')
     def __project_to_dn(self, pid, search=True):
         """Convert pid to dn"""
         # By default return a generated DN
@@ -603,16 +665,18 @@ class LdapDriver(object):
         else:
             return None
 
+    @__local_cache('dn_uid-%s')
     def __dn_to_uid(self, dn):
         """Convert user dn to uid"""
         query = '(objectclass=novaUser)'
-        user = self.__find_object(dn, query)
+        user = self.__find_object(dn, query, scope=self.ldap.SCOPE_BASE)
         return user[FLAGS.ldap_user_id_attribute][0]
 
 
 class FakeLdapDriver(LdapDriver):
     """Fake Ldap Auth driver"""
 
-    def __init__(self):  # pylint: disable=W0231
-        __import__('nova.auth.fakeldap')
-        self.ldap = sys.modules['nova.auth.fakeldap']
+    def __init__(self):
+        import nova.auth.fakeldap
+        sys.modules['ldap'] = nova.auth.fakeldap
+        super(FakeLdapDriver, self).__init__()
diff --git a/nova/auth/manager.py b/nova/auth/manager.py
index 07235a2a7..98c7dd263 100644
--- a/nova/auth/manager.py
+++ b/nova/auth/manager.py
@@ -73,6 +73,12 @@ flags.DEFINE_string('auth_driver', 'nova.auth.dbdriver.DbDriver',
 LOG = logging.getLogger('nova.auth.manager')
 
 
+if FLAGS.memcached_servers:
+    import memcache
+else:
+    from nova import fakememcache as memcache
+
+
 class AuthBase(object):
     """Base class for objects relating to auth
 
@@ -206,6 +212,7 @@ class AuthManager(object):
     """
 
     _instance = None
+    mc = None
 
     def __new__(cls, *args, **kwargs):
         """Returns the AuthManager singleton"""
@@ -222,13 +229,8 @@ class AuthManager(object):
         self.network_manager = utils.import_object(FLAGS.network_manager)
         if driver or not getattr(self, 'driver', None):
             self.driver = utils.import_class(driver or FLAGS.auth_driver)
-
-        if FLAGS.memcached_servers:
-            import memcache
-        else:
-            from nova import fakememcache as memcache
-        self.mc = memcache.Client(FLAGS.memcached_servers,
-                                  debug=0)
+        if AuthManager.mc is None:
+            AuthManager.mc = memcache.Client(FLAGS.memcached_servers, debug=0)
 
     def authenticate(self, access, signature, params, verb='GET',
                      server_string='127.0.0.1:8773', path='/',
diff --git a/nova/compute/api.py b/nova/compute/api.py
index ea4cb8036..4f327fab1 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -18,7 +18,6 @@
 
 """Handles all requests relating to instances (guest vms)."""
 
-import datetime
 import eventlet
 import re
 import time
@@ -407,7 +406,7 @@ class API(base.Base):
                     instance['id'],
                     state_description='terminating',
                     state=0,
-                    terminated_at=datetime.datetime.utcnow())
+                    terminated_at=utils.utcnow())
 
         host = instance['host']
         if host:
diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 7fe5fa2cb..245958de7 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -35,7 +35,6 @@ terminating it.
 
 """
 
-import datetime
 import os
 import socket
 import sys
@@ -159,7 +158,7 @@ class ComputeManager(manager.SchedulerDependentManager):
 
     def _update_launched_at(self, context, instance_id, launched_at=None):
         """Update the launched_at parameter of the given instance."""
-        data = {'launched_at': launched_at or datetime.datetime.utcnow()}
+        data = {'launched_at': launched_at or utils.utcnow()}
         self.db.instance_update(context, instance_id, data)
 
     def _update_image_ref(self, context, instance_id, image_ref):
diff --git a/nova/compute/monitor.py b/nova/compute/monitor.py
index 3bb54a382..613734bef 100644
--- a/nova/compute/monitor.py
+++ b/nova/compute/monitor.py
@@ -86,7 +86,7 @@ RRD_VALUES = {
         ]}
 
 
-utcnow = datetime.datetime.utcnow
+utcnow = utils.utcnow
 
 
 LOG = logging.getLogger('nova.compute.monitor')
diff --git a/nova/context.py b/nova/context.py
index c113f7ea7..99085ed75 100644
--- a/nova/context.py
+++ b/nova/context.py
@@ -18,7 +18,6 @@
 
 """RequestContext: context for requests that persist through all of nova."""
 
-import datetime
 import random
 
 from nova import exception
diff --git a/nova/db/sqlalchemy/api.py b/nova/db/sqlalchemy/api.py
index 6970a2168..86423e905 100644
--- a/nova/db/sqlalchemy/api.py
+++ b/nova/db/sqlalchemy/api.py
@@ -19,7 +19,6 @@
 Implementation of SQLAlchemy backend.
 """
 
-import datetime
 import warnings
 
 from nova import db
@@ -674,7 +673,7 @@ def fixed_ip_disassociate_all_by_timeout(_context, host, time):
                      filter_by(allocated=0).\
                      update({'instance_id': None,
                              'leased': 0,
-                             'updated_at': datetime.datetime.utcnow()},
+                             'updated_at': utils.utcnow()},
                              synchronize_session='fetch')
     return result
 
@@ -820,17 +819,17 @@ def instance_destroy(context, instance_id):
         session.query(models.Instance).\
                 filter_by(id=instance_id).\
                 update({'deleted': True,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.SecurityGroupInstanceAssociation).\
                 filter_by(instance_id=instance_id).\
                 update({'deleted': True,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.InstanceMetadata).\
                 filter_by(instance_id=instance_id).\
                 update({'deleted': True,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
 
 
@@ -1123,7 +1122,7 @@ def key_pair_destroy_all_by_user(context, user_id):
         session.query(models.KeyPair).\
                 filter_by(user_id=user_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
 
 
@@ -1655,7 +1654,7 @@ def volume_destroy(context, volume_id):
         session.query(models.Volume).\
                 filter_by(id=volume_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.ExportDevice).\
                 filter_by(volume_id=volume_id).\
@@ -1813,7 +1812,7 @@ def snapshot_destroy(context, snapshot_id):
         session.query(models.Snapshot).\
                 filter_by(id=snapshot_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
 
 
@@ -1968,17 +1967,17 @@ def security_group_destroy(context, security_group_id):
         session.query(models.SecurityGroup).\
                 filter_by(id=security_group_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.SecurityGroupInstanceAssociation).\
                 filter_by(security_group_id=security_group_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.SecurityGroupIngressRule).\
                 filter_by(group_id=security_group_id).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
 
 
@@ -1989,11 +1988,11 @@ def security_group_destroy_all(context, session=None):
     with session.begin():
         session.query(models.SecurityGroup).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
         session.query(models.SecurityGroupIngressRule).\
                 update({'deleted': 1,
-                        'deleted_at': datetime.datetime.utcnow(),
+                        'deleted_at': utils.utcnow(),
                         'updated_at': literal_column('updated_at')})
 
 
@@ -2627,7 +2626,7 @@ def instance_metadata_delete(context, instance_id, key):
         filter_by(key=key).\
         filter_by(deleted=False).\
         update({'deleted': True,
-                'deleted_at': datetime.datetime.utcnow(),
+                'deleted_at': utils.utcnow(),
                 'updated_at': literal_column('updated_at')})
 
 
@@ -2638,7 +2637,7 @@ def instance_metadata_delete_all(context, instance_id):
         filter_by(instance_id=instance_id).\
         filter_by(deleted=False).\
         update({'deleted': True,
-                'deleted_at': datetime.datetime.utcnow(),
+                'deleted_at': utils.utcnow(),
                 'updated_at': literal_column('updated_at')})
 
 
diff --git a/nova/db/sqlalchemy/migrate_repo/versions/016_make_quotas_key_and_value.py b/nova/db/sqlalchemy/migrate_repo/versions/016_make_quotas_key_and_value.py
index 5d0593f2e..a4fe3e482 100644
--- a/nova/db/sqlalchemy/migrate_repo/versions/016_make_quotas_key_and_value.py
+++ b/nova/db/sqlalchemy/migrate_repo/versions/016_make_quotas_key_and_value.py
@@ -17,7 +17,7 @@
 from sqlalchemy import Boolean, Column, DateTime, Integer
 from sqlalchemy import MetaData, String, Table
 
-import datetime
+from nova import utils
 
 meta = MetaData()
 
@@ -35,9 +35,9 @@ def old_style_quotas_table(name):
     return Table(name, meta,
                  Column('id', Integer(), primary_key=True),
                  Column('created_at', DateTime(),
-                        default=datetime.datetime.utcnow),
+                        default=utils.utcnow),
                  Column('updated_at', DateTime(),
-                        onupdate=datetime.datetime.utcnow),
+                        onupdate=utils.utcnow),
                  Column('deleted_at', DateTime()),
                  Column('deleted', Boolean(), default=False),
                  Column('project_id',
@@ -57,9 +57,9 @@ def new_style_quotas_table(name):
     return Table(name, meta,
                  Column('id', Integer(), primary_key=True),
                  Column('created_at', DateTime(),
-                        default=datetime.datetime.utcnow),
+                        default=utils.utcnow),
                  Column('updated_at', DateTime(),
-                        onupdate=datetime.datetime.utcnow),
+                        onupdate=utils.utcnow),
                  Column('deleted_at', DateTime()),
                  Column('deleted', Boolean(), default=False),
                  Column('project_id',
diff --git a/nova/db/sqlalchemy/models.py b/nova/db/sqlalchemy/models.py
index 82b521e77..239f6e96a 100644
--- a/nova/db/sqlalchemy/models.py
+++ b/nova/db/sqlalchemy/models.py
@@ -19,8 +19,6 @@
 SQLAlchemy models for nova data.
 """
 
-import datetime
-
 from sqlalchemy.orm import relationship, backref, object_mapper
 from sqlalchemy import Column, Integer, String, schema
 from sqlalchemy import ForeignKey, DateTime, Boolean, Text
@@ -33,6 +31,7 @@ from nova.db.sqlalchemy.session import get_session
 from nova import auth
 from nova import exception
 from nova import flags
+from nova import utils
 
 
 FLAGS = flags.FLAGS
@@ -43,8 +42,8 @@ class NovaBase(object):
     """Base class for Nova Models."""
     __table_args__ = {'mysql_engine': 'InnoDB'}
     __table_initialized__ = False
-    created_at = Column(DateTime, default=datetime.datetime.utcnow)
-    updated_at = Column(DateTime, onupdate=datetime.datetime.utcnow)
+    created_at = Column(DateTime, default=utils.utcnow)
+    updated_at = Column(DateTime, onupdate=utils.utcnow)
     deleted_at = Column(DateTime)
     deleted = Column(Boolean, default=False)
     metadata = None
@@ -65,7 +64,7 @@ class NovaBase(object):
     def delete(self, session=None):
         """Delete this object."""
         self.deleted = True
-        self.deleted_at = datetime.datetime.utcnow()
+        self.deleted_at = utils.utcnow()
         self.save(session=session)
 
     def __setitem__(self, key, value):
diff --git a/nova/exception.py b/nova/exception.py
index eaafa7692..69b3e0359 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -486,6 +486,15 @@ class SchedulerHostFilterNotFound(NotFound):
     message = _("Scheduler Host Filter %(filter_name)s could not be found.")
 
 
+class SchedulerCostFunctionNotFound(NotFound):
+    message = _("Scheduler cost function %(cost_fn_str)s could"
+                " not be found.")
+
+
+class SchedulerWeightFlagNotFound(NotFound):
+    message = _("Scheduler weight flag not found: %(flag_name)s")
+
+
 class InstanceMetadataNotFound(NotFound):
     message = _("Instance %(instance_id)s has no metadata with "
                 "key %(metadata_key)s.")
diff --git a/nova/network/manager.py b/nova/network/manager.py
index 5a6fdde5a..f726c4b26 100644
--- a/nova/network/manager.py
+++ b/nova/network/manager.py
@@ -235,7 +235,7 @@ class NetworkManager(manager.SchedulerDependentManager):
             inst_addr = instance_ref['mac_address']
             raise exception.Error(_('IP %(address)s leased to bad mac'
                                     ' %(inst_addr)s vs %(mac)s') % locals())
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         self.db.fixed_ip_update(context,
                                 fixed_ip_ref['address'],
                                 {'leased': True,
diff --git a/nova/notifier/api.py b/nova/notifier/api.py
index a3e7a039e..d49517c8b 100644
--- a/nova/notifier/api.py
+++ b/nova/notifier/api.py
@@ -11,9 +11,8 @@
 #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
-#    under the License.import datetime
+#    under the License.
 
-import datetime
 import uuid
 
 from nova import flags
@@ -64,7 +63,7 @@ def notify(publisher_id, event_type, priority, payload):
 
     {'message_id': str(uuid.uuid4()),
      'publisher_id': 'compute.host1',
-     'timestamp': datetime.datetime.utcnow(),
+     'timestamp': utils.utcnow(),
      'priority': 'WARN',
      'event_type': 'compute.create_instance',
      'payload': {'instance_id': 12, ... }}
@@ -79,5 +78,5 @@ def notify(publisher_id, event_type, priority, payload):
                    event_type=event_type,
                    priority=priority,
                    payload=payload,
-                   timestamp=str(datetime.datetime.utcnow()))
+                   timestamp=str(utils.utcnow()))
     driver.notify(msg)
diff --git a/nova/scheduler/driver.py b/nova/scheduler/driver.py
index 2094e3565..0b257c5d8 100644
--- a/nova/scheduler/driver.py
+++ b/nova/scheduler/driver.py
@@ -28,6 +28,7 @@ from nova import exception
 from nova import flags
 from nova import log as logging
 from nova import rpc
+from nova import utils
 from nova.compute import power_state
 
 FLAGS = flags.FLAGS
@@ -61,7 +62,7 @@ class Scheduler(object):
         """Check whether a service is up based on last heartbeat."""
         last_heartbeat = service['updated_at'] or service['created_at']
         # Timestamps in DB are UTC.
-        elapsed = datetime.datetime.utcnow() - last_heartbeat
+        elapsed = utils.utcnow() - last_heartbeat
         return elapsed < datetime.timedelta(seconds=FLAGS.service_down_time)
 
     def hosts_up(self, context, topic):
diff --git a/nova/scheduler/host_filter.py b/nova/scheduler/host_filter.py
index 7d6ee0ee3..bd6b26608 100644
--- a/nova/scheduler/host_filter.py
+++ b/nova/scheduler/host_filter.py
@@ -41,6 +41,7 @@ import json
 from nova import exception
 from nova import flags
 from nova import log as logging
+from nova.scheduler import zone_aware_scheduler
 from nova import utils
 from nova.scheduler import zone_aware_scheduler
 
diff --git a/nova/scheduler/least_cost.py b/nova/scheduler/least_cost.py
new file mode 100644
index 000000000..629fe2e42
--- /dev/null
+++ b/nova/scheduler/least_cost.py
@@ -0,0 +1,156 @@
+# Copyright (c) 2011 Openstack, LLC.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""
+Least Cost Scheduler is a mechanism for choosing which host machines to
+provision a set of resources to. The input of the least-cost-scheduler is a
+set of objective-functions, called the 'cost-functions', a weight for each
+cost-function, and a list of candidate hosts (gathered via FilterHosts).
+
+The cost-function and weights are tabulated, and the host with the least cost
+is then selected for provisioning.
+"""
+
+import collections
+
+from nova import flags
+from nova import log as logging
+from nova.scheduler import zone_aware_scheduler
+from nova import utils
+
+LOG = logging.getLogger('nova.scheduler.least_cost')
+
+FLAGS = flags.FLAGS
+flags.DEFINE_list('least_cost_scheduler_cost_functions',
+                  ['nova.scheduler.least_cost.noop_cost_fn'],
+                  'Which cost functions the LeastCostScheduler should use.')
+
+
+# TODO(sirp): Once we have enough of these rules, we can break them out into a
+# cost_functions.py file (perhaps in a least_cost_scheduler directory)
+flags.DEFINE_integer('noop_cost_fn_weight', 1,
+                     'How much weight to give the noop cost function')
+
+
+def noop_cost_fn(host):
+    """Return a pre-weight cost of 1 for each host"""
+    return 1
+
+
+flags.DEFINE_integer('fill_first_cost_fn_weight', 1,
+                     'How much weight to give the fill-first cost function')
+
+
+def fill_first_cost_fn(host):
+    """Prefer hosts that have less ram available, filter_hosts will exclude
+    hosts that don't have enough ram"""
+    hostname, caps = host
+    free_mem = caps['compute']['host_memory_free']
+    return free_mem
+
+
+class LeastCostScheduler(zone_aware_scheduler.ZoneAwareScheduler):
+    def get_cost_fns(self):
+        """Returns a list of tuples containing weights and cost functions to
+        use for weighing hosts
+        """
+        cost_fns = []
+        for cost_fn_str in FLAGS.least_cost_scheduler_cost_functions:
+
+            try:
+                # NOTE(sirp): import_class is somewhat misnamed since it can
+                # any callable from a module
+                cost_fn = utils.import_class(cost_fn_str)
+            except exception.ClassNotFound:
+                raise exception.SchedulerCostFunctionNotFound(
+                    cost_fn_str=cost_fn_str)
+
+            try:
+                weight = getattr(FLAGS, "%s_weight" % cost_fn.__name__)
+            except AttributeError:
+                raise exception.SchedulerWeightFlagNotFound(
+                    flag_name=flag_name)
+
+            cost_fns.append((weight, cost_fn))
+
+        return cost_fns
+
+    def weigh_hosts(self, num, request_spec, hosts):
+        """Returns a list of dictionaries of form:
+            [ {weight: weight, hostname: hostname} ]"""
+
+        # FIXME(sirp): weigh_hosts should handle more than just instances
+        hostnames = [hostname for hostname, caps in hosts]
+
+        cost_fns = self.get_cost_fns()
+        costs = weighted_sum(domain=hosts, weighted_fns=cost_fns)
+
+        weighted = []
+        weight_log = []
+        for cost, hostname in zip(costs, hostnames):
+            weight_log.append("%s: %s" % (hostname, "%.2f" % cost))
+            weight_dict = dict(weight=cost, hostname=hostname)
+            weighted.append(weight_dict)
+
+        LOG.debug(_("Weighted Costs => %s") % weight_log)
+        return weighted
+
+
+def normalize_list(L):
+    """Normalize an array of numbers such that each element satisfies:
+        0 <= e <= 1"""
+    if not L:
+        return L
+    max_ = max(L)
+    if max_ > 0:
+        return [(float(e) / max_) for e in L]
+    return L
+
+
+def weighted_sum(domain, weighted_fns, normalize=True):
+    """Use the weighted-sum method to compute a score for an array of objects.
+    Normalize the results of the objective-functions so that the weights are
+    meaningful regardless of objective-function's range.
+
+    domain - input to be scored
+    weighted_fns - list of weights and functions like:
+        [(weight, objective-functions)]
+
+    Returns an unsorted of scores. To pair with hosts do: zip(scores, hosts)
+    """
+    # Table of form:
+    #   { domain1: [score1, score2, ..., scoreM]
+    #     ...
+    #     domainN: [score1, score2, ..., scoreM] }
+    score_table = collections.defaultdict(list)
+    for weight, fn in weighted_fns:
+        scores = [fn(elem) for elem in domain]
+
+        if normalize:
+            norm_scores = normalize_list(scores)
+        else:
+            norm_scores = scores
+
+        for idx, score in enumerate(norm_scores):
+            weighted_score = score * weight
+            score_table[idx].append(weighted_score)
+
+    # Sum rows in table to compute score for each element in domain
+    domain_scores = []
+    for idx in sorted(score_table):
+        elem_score = sum(score_table[idx])
+        elem = domain[idx]
+        domain_scores.append(elem_score)
+
+    return domain_scores
diff --git a/nova/scheduler/simple.py b/nova/scheduler/simple.py
index dd568d2c6..87cdef11d 100644
--- a/nova/scheduler/simple.py
+++ b/nova/scheduler/simple.py
@@ -21,10 +21,9 @@
 Simple Scheduler
 """
 
-import datetime
-
 from nova import db
 from nova import flags
+from nova import utils
 from nova.scheduler import driver
 from nova.scheduler import chance
 
@@ -54,7 +53,7 @@ class SimpleScheduler(chance.ChanceScheduler):
 
             # TODO(vish): this probably belongs in the manager, if we
             #             can generalize this somehow
-            now = datetime.datetime.utcnow()
+            now = utils.utcnow()
             db.instance_update(context, instance_id, {'host': host,
                                                       'scheduled_at': now})
             return host
@@ -66,7 +65,7 @@ class SimpleScheduler(chance.ChanceScheduler):
             if self.service_is_up(service):
                 # NOTE(vish): this probably belongs in the manager, if we
                 #             can generalize this somehow
-                now = datetime.datetime.utcnow()
+                now = utils.utcnow()
                 db.instance_update(context,
                                    instance_id,
                                    {'host': service['host'],
@@ -90,7 +89,7 @@ class SimpleScheduler(chance.ChanceScheduler):
 
             # TODO(vish): this probably belongs in the manager, if we
             #             can generalize this somehow
-            now = datetime.datetime.utcnow()
+            now = utils.utcnow()
             db.volume_update(context, volume_id, {'host': host,
                                                   'scheduled_at': now})
             return host
@@ -103,7 +102,7 @@ class SimpleScheduler(chance.ChanceScheduler):
             if self.service_is_up(service):
                 # NOTE(vish): this probably belongs in the manager, if we
                 #             can generalize this somehow
-                now = datetime.datetime.utcnow()
+                now = utils.utcnow()
                 db.volume_update(context,
                                  volume_id,
                                  {'host': service['host'],
diff --git a/nova/scheduler/zone_aware_scheduler.py b/nova/scheduler/zone_aware_scheduler.py
index bc67c7794..df84cf7bd 100644
--- a/nova/scheduler/zone_aware_scheduler.py
+++ b/nova/scheduler/zone_aware_scheduler.py
@@ -39,7 +39,7 @@ class ZoneAwareScheduler(driver.Scheduler):
         return api.call_zone_method(context, method, specs=specs)
 
     def schedule_run_instance(self, context, instance_id, request_spec,
-                                        *args, **kwargs):
+                              *args, **kwargs):
         """This method is called from nova.compute.api to provision
         an instance. However we need to look at the parameters being
         passed in to see if this is a request to:
@@ -116,6 +116,9 @@ class ZoneAwareScheduler(driver.Scheduler):
         # Filter local hosts based on requirements ...
         host_list = self.filter_hosts(num_instances, request_spec)
 
+        # TODO(sirp): weigh_hosts should also be a function of 'topic' or
+        # resources, so that we can apply different objective functions to it
+
         # then weigh the selected hosts.
         # weighted = [{weight=weight, name=hostname}, ...]
         weighted = self.weigh_hosts(num_instances, request_spec, host_list)
@@ -139,12 +142,16 @@ class ZoneAwareScheduler(driver.Scheduler):
 
     def filter_hosts(self, num, request_spec):
         """Derived classes must override this method and return
-        a list of hosts in [(hostname, capability_dict)] format.
+           a list of hosts in [(hostname, capability_dict)] format.
         """
-        raise NotImplemented()
+        # NOTE(sirp): The default logic is the equivalent to AllHostsFilter
+        service_states = self.zone_manager.service_states
+        return [(host, services)
+                for host, services in service_states.iteritems()]
 
     def weigh_hosts(self, num, request_spec, hosts):
-        """Derived classes must override this method and return
-        a lists of hosts in [{weight, hostname}] format.
+        """Derived classes may override this to provide more sophisticated
+        scheduling objectives
         """
-        raise NotImplemented()
+        # NOTE(sirp): The default logic is the same as the NoopCostFunction
+        return [dict(weight=1, hostname=host) for host, caps in hosts]
diff --git a/nova/scheduler/zone_manager.py b/nova/scheduler/zone_manager.py
index 3ddf6f3c3..3f483adff 100644
--- a/nova/scheduler/zone_manager.py
+++ b/nova/scheduler/zone_manager.py
@@ -17,16 +17,17 @@
 ZoneManager oversees all communications with child Zones.
 """
 
+import datetime
 import novaclient
 import thread
 import traceback
 
-from datetime import datetime
 from eventlet import greenpool
 
 from nova import db
 from nova import flags
 from nova import log as logging
+from nova import utils
 
 FLAGS = flags.FLAGS
 flags.DEFINE_integer('zone_db_check_interval', 60,
@@ -42,7 +43,7 @@ class ZoneState(object):
         self.name = None
         self.capabilities = None
         self.attempt = 0
-        self.last_seen = datetime.min
+        self.last_seen = datetime.datetime.min
         self.last_exception = None
         self.last_exception_time = None
 
@@ -56,7 +57,7 @@ class ZoneState(object):
     def update_metadata(self, zone_metadata):
         """Update zone metadata after successful communications with
            child zone."""
-        self.last_seen = datetime.now()
+        self.last_seen = utils.utcnow()
         self.attempt = 0
         self.name = zone_metadata.get("name", "n/a")
         self.capabilities = ", ".join(["%s=%s" % (k, v)
@@ -72,7 +73,7 @@ class ZoneState(object):
         """Something went wrong. Check to see if zone should be
            marked as offline."""
         self.last_exception = exception
-        self.last_exception_time = datetime.now()
+        self.last_exception_time = utils.utcnow()
         api_url = self.api_url
         logging.warning(_("'%(exception)s' error talking to "
                           "zone %(api_url)s") % locals())
@@ -104,7 +105,7 @@ def _poll_zone(zone):
 class ZoneManager(object):
     """Keeps the zone states updated."""
     def __init__(self):
-        self.last_zone_db_check = datetime.min
+        self.last_zone_db_check = datetime.datetime.min
         self.zone_states = {}  # { <zone_id> : ZoneState }
         self.service_states = {}  # { <host> : { <service> : { cap k : v }}}
         self.green_pool = greenpool.GreenPool()
@@ -158,10 +159,10 @@ class ZoneManager(object):
 
     def ping(self, context=None):
         """Ping should be called periodically to update zone status."""
-        diff = datetime.now() - self.last_zone_db_check
+        diff = utils.utcnow() - self.last_zone_db_check
         if diff.seconds >= FLAGS.zone_db_check_interval:
             logging.debug(_("Updating zone cache from db."))
-            self.last_zone_db_check = datetime.now()
+            self.last_zone_db_check = utils.utcnow()
             self._refresh_from_db(context)
         self._poll_zones(context)
 
diff --git a/nova/test.py b/nova/test.py
index 80b2d0a74..4a0a18fe7 100644
--- a/nova/test.py
+++ b/nova/test.py
@@ -23,7 +23,6 @@ inline callbacks.
 
 """
 
-import datetime
 import functools
 import os
 import shutil
@@ -37,6 +36,7 @@ from eventlet import greenthread
 from nova import fakerabbit
 from nova import flags
 from nova import rpc
+from nova import utils
 from nova import service
 from nova import wsgi
 from nova.virt import fake
@@ -69,7 +69,7 @@ class TestCase(unittest.TestCase):
         # NOTE(vish): We need a better method for creating fixtures for tests
         #             now that we have some required db setup for the system
         #             to work properly.
-        self.start = datetime.datetime.utcnow()
+        self.start = utils.utcnow()
         shutil.copyfile(os.path.join(FLAGS.state_path, FLAGS.sqlite_clean_db),
                         os.path.join(FLAGS.state_path, FLAGS.sqlite_db))
 
@@ -184,7 +184,7 @@ class TestCase(unittest.TestCase):
         wsgi.Server.start = _wrapped_start
 
     # Useful assertions
-    def assertDictMatch(self, d1, d2):
+    def assertDictMatch(self, d1, d2, approx_equal=False, tolerance=0.001):
         """Assert two dicts are equivalent.
 
         This is a 'deep' match in the sense that it handles nested
@@ -215,15 +215,26 @@ class TestCase(unittest.TestCase):
         for key in d1keys:
             d1value = d1[key]
             d2value = d2[key]
+            try:
+                error = abs(float(d1value) - float(d2value))
+                within_tolerance = error <= tolerance
+            except (ValueError, TypeError):
+                # If both values aren't convertable to float, just ignore
+                # ValueError if arg is a str, TypeError if it's something else
+                # (like None)
+                within_tolerance = False
+
             if hasattr(d1value, 'keys') and hasattr(d2value, 'keys'):
                 self.assertDictMatch(d1value, d2value)
             elif 'DONTCARE' in (d1value, d2value):
                 continue
+            elif approx_equal and within_tolerance:
+                continue
             elif d1value != d2value:
                 raise_assertion("d1['%(key)s']=%(d1value)s != "
                                 "d2['%(key)s']=%(d2value)s" % locals())
 
-    def assertDictListMatch(self, L1, L2):
+    def assertDictListMatch(self, L1, L2, approx_equal=False, tolerance=0.001):
         """Assert a list of dicts are equivalent."""
         def raise_assertion(msg):
             L1str = str(L1)
@@ -239,4 +250,5 @@ class TestCase(unittest.TestCase):
                             'len(L2)=%(L2count)d' % locals())
 
         for d1, d2 in zip(L1, L2):
-            self.assertDictMatch(d1, d2)
+            self.assertDictMatch(d1, d2, approx_equal=approx_equal,
+                                 tolerance=tolerance)
diff --git a/nova/tests/api/openstack/fakes.py b/nova/tests/api/openstack/fakes.py
index 17d6d591c..62e44ba96 100644
--- a/nova/tests/api/openstack/fakes.py
+++ b/nova/tests/api/openstack/fakes.py
@@ -16,7 +16,6 @@
 #    under the License.
 
 import copy
-import datetime
 import json
 import random
 import string
@@ -256,7 +255,7 @@ class FakeAuthDatabase(object):
 
     @staticmethod
     def auth_token_create(context, token):
-        fake_token = FakeToken(created_at=datetime.datetime.now(), **token)
+        fake_token = FakeToken(created_at=utils.utcnow(), **token)
         FakeAuthDatabase.data[fake_token.token_hash] = fake_token
         FakeAuthDatabase.data['id_%i' % fake_token.id] = fake_token
         return fake_token
diff --git a/nova/tests/api/openstack/test_images.py b/nova/tests/api/openstack/test_images.py
index 9f1f28611..93b402081 100644
--- a/nova/tests/api/openstack/test_images.py
+++ b/nova/tests/api/openstack/test_images.py
@@ -22,7 +22,6 @@ and as a WSGI layer
 
 import copy
 import json
-import datetime
 import os
 import shutil
 import tempfile
diff --git a/nova/tests/api/openstack/test_servers.py b/nova/tests/api/openstack/test_servers.py
index 3acdf3816..28ad4a417 100644
--- a/nova/tests/api/openstack/test_servers.py
+++ b/nova/tests/api/openstack/test_servers.py
@@ -16,7 +16,6 @@
 #    under the License.
 
 import base64
-import datetime
 import json
 import unittest
 from xml.dom import minidom
@@ -29,6 +28,7 @@ from nova import db
 from nova import exception
 from nova import flags
 from nova import test
+from nova import utils
 import nova.api.openstack
 from nova.api.openstack import servers
 import nova.compute.api
@@ -115,9 +115,9 @@ def stub_instance(id, user_id=1, private_address=None, public_addresses=None,
         "user_data": "",
         "reservation_id": "",
         "mac_address": "",
-        "scheduled_at": datetime.datetime.now(),
-        "launched_at": datetime.datetime.now(),
-        "terminated_at": datetime.datetime.now(),
+        "scheduled_at": utils.utcnow(),
+        "launched_at": utils.utcnow(),
+        "terminated_at": utils.utcnow(),
         "availability_zone": "",
         "display_name": "server%s" % id,
         "display_description": "",
diff --git a/nova/tests/scheduler/__init__.py b/nova/tests/scheduler/__init__.py
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/nova/tests/scheduler/__init__.py
diff --git a/nova/tests/scheduler/test_host_filter.py b/nova/tests/scheduler/test_host_filter.py
new file mode 100644
index 000000000..07817cc5a
--- /dev/null
+++ b/nova/tests/scheduler/test_host_filter.py
@@ -0,0 +1,206 @@
+# Copyright 2011 OpenStack LLC.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""
+Tests For Scheduler Host Filters.
+"""
+
+import json
+
+from nova import exception
+from nova import flags
+from nova import test
+from nova.scheduler import host_filter
+
+FLAGS = flags.FLAGS
+
+
+class FakeZoneManager:
+    pass
+
+
+class HostFilterTestCase(test.TestCase):
+    """Test case for host filters."""
+
+    def _host_caps(self, multiplier):
+        # Returns host capabilities in the following way:
+        # host1 = memory:free 10 (100max)
+        #         disk:available 100 (1000max)
+        # hostN = memory:free 10 + 10N
+        #         disk:available 100 + 100N
+        # in other words: hostN has more resources than host0
+        # which means ... don't go above 10 hosts.
+        return {'host_name-description': 'XenServer %s' % multiplier,
+                'host_hostname': 'xs-%s' % multiplier,
+                'host_memory_total': 100,
+                'host_memory_overhead': 10,
+                'host_memory_free': 10 + multiplier * 10,
+                'host_memory_free-computed': 10 + multiplier * 10,
+                'host_other-config': {},
+                'host_ip_address': '192.168.1.%d' % (100 + multiplier),
+                'host_cpu_info': {},
+                'disk_available': 100 + multiplier * 100,
+                'disk_total': 1000,
+                'disk_used': 0,
+                'host_uuid': 'xxx-%d' % multiplier,
+                'host_name-label': 'xs-%s' % multiplier}
+
+    def setUp(self):
+        self.old_flag = FLAGS.default_host_filter
+        FLAGS.default_host_filter = \
+                            'nova.scheduler.host_filter.AllHostsFilter'
+        self.instance_type = dict(name='tiny',
+                memory_mb=50,
+                vcpus=10,
+                local_gb=500,
+                flavorid=1,
+                swap=500,
+                rxtx_quota=30000,
+                rxtx_cap=200)
+
+        self.zone_manager = FakeZoneManager()
+        states = {}
+        for x in xrange(10):
+            states['host%02d' % (x + 1)] = {'compute': self._host_caps(x)}
+        self.zone_manager.service_states = states
+
+    def tearDown(self):
+        FLAGS.default_host_filter = self.old_flag
+
+    def test_choose_filter(self):
+        # Test default filter ...
+        hf = host_filter.choose_host_filter()
+        self.assertEquals(hf._full_name(),
+                        'nova.scheduler.host_filter.AllHostsFilter')
+        # Test valid filter ...
+        hf = host_filter.choose_host_filter(
+                        'nova.scheduler.host_filter.InstanceTypeFilter')
+        self.assertEquals(hf._full_name(),
+                        'nova.scheduler.host_filter.InstanceTypeFilter')
+        # Test invalid filter ...
+        try:
+            host_filter.choose_host_filter('does not exist')
+            self.fail("Should not find host filter.")
+        except exception.SchedulerHostFilterNotFound:
+            pass
+
+    def test_all_host_filter(self):
+        hf = host_filter.AllHostsFilter()
+        cooked = hf.instance_type_to_filter(self.instance_type)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+        self.assertEquals(10, len(hosts))
+        for host, capabilities in hosts:
+            self.assertTrue(host.startswith('host'))
+
+    def test_instance_type_filter(self):
+        hf = host_filter.InstanceTypeFilter()
+        # filter all hosts that can support 50 ram and 500 disk
+        name, cooked = hf.instance_type_to_filter(self.instance_type)
+        self.assertEquals('nova.scheduler.host_filter.InstanceTypeFilter',
+                          name)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+        self.assertEquals(6, len(hosts))
+        just_hosts = [host for host, caps in hosts]
+        just_hosts.sort()
+        self.assertEquals('host05', just_hosts[0])
+        self.assertEquals('host10', just_hosts[5])
+
+    def test_json_filter(self):
+        hf = host_filter.JsonFilter()
+        # filter all hosts that can support 50 ram and 500 disk
+        name, cooked = hf.instance_type_to_filter(self.instance_type)
+        self.assertEquals('nova.scheduler.host_filter.JsonFilter', name)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+        self.assertEquals(6, len(hosts))
+        just_hosts = [host for host, caps in hosts]
+        just_hosts.sort()
+        self.assertEquals('host05', just_hosts[0])
+        self.assertEquals('host10', just_hosts[5])
+
+        # Try some custom queries
+
+        raw = ['or',
+                   ['and',
+                       ['<', '$compute.host_memory_free', 30],
+                       ['<', '$compute.disk_available', 300]
+                   ],
+                   ['and',
+                       ['>', '$compute.host_memory_free', 70],
+                       ['>', '$compute.disk_available', 700]
+                   ]
+              ]
+        cooked = json.dumps(raw)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+
+        self.assertEquals(5, len(hosts))
+        just_hosts = [host for host, caps in hosts]
+        just_hosts.sort()
+        for index, host in zip([1, 2, 8, 9, 10], just_hosts):
+            self.assertEquals('host%02d' % index, host)
+
+        raw = ['not',
+                  ['=', '$compute.host_memory_free', 30],
+              ]
+        cooked = json.dumps(raw)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+
+        self.assertEquals(9, len(hosts))
+        just_hosts = [host for host, caps in hosts]
+        just_hosts.sort()
+        for index, host in zip([1, 2, 4, 5, 6, 7, 8, 9, 10], just_hosts):
+            self.assertEquals('host%02d' % index, host)
+
+        raw = ['in', '$compute.host_memory_free', 20, 40, 60, 80, 100]
+        cooked = json.dumps(raw)
+        hosts = hf.filter_hosts(self.zone_manager, cooked)
+
+        self.assertEquals(5, len(hosts))
+        just_hosts = [host for host, caps in hosts]
+        just_hosts.sort()
+        for index, host in zip([2, 4, 6, 8, 10], just_hosts):
+            self.assertEquals('host%02d' % index, host)
+
+        # Try some bogus input ...
+        raw = ['unknown command', ]
+        cooked = json.dumps(raw)
+        try:
+            hf.filter_hosts(self.zone_manager, cooked)
+            self.fail("Should give KeyError")
+        except KeyError, e:
+            pass
+
+        self.assertTrue(hf.filter_hosts(self.zone_manager, json.dumps([])))
+        self.assertTrue(hf.filter_hosts(self.zone_manager, json.dumps({})))
+        self.assertTrue(hf.filter_hosts(self.zone_manager, json.dumps(
+                ['not', True, False, True, False]
+            )))
+
+        try:
+            hf.filter_hosts(self.zone_manager, json.dumps(
+                'not', True, False, True, False
+            ))
+            self.fail("Should give KeyError")
+        except KeyError, e:
+            pass
+
+        self.assertFalse(hf.filter_hosts(self.zone_manager,
+                json.dumps(['=', '$foo', 100])))
+        self.assertFalse(hf.filter_hosts(self.zone_manager,
+                json.dumps(['=', '$.....', 100])))
+        self.assertFalse(hf.filter_hosts(self.zone_manager,
+                json.dumps(
+            ['>', ['and', ['or', ['not', ['<', ['>=', ['<=', ['in', ]]]]]]]])))
+
+        self.assertFalse(hf.filter_hosts(self.zone_manager,
+                json.dumps(['=', {}, ['>', '$missing....foo']])))
diff --git a/nova/tests/scheduler/test_least_cost_scheduler.py b/nova/tests/scheduler/test_least_cost_scheduler.py
new file mode 100644
index 000000000..506fa62fb
--- /dev/null
+++ b/nova/tests/scheduler/test_least_cost_scheduler.py
@@ -0,0 +1,144 @@
+# Copyright 2011 OpenStack LLC.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""
+Tests For Least Cost Scheduler
+"""
+
+from nova import flags
+from nova import test
+from nova.scheduler import least_cost
+from nova.tests.scheduler import test_zone_aware_scheduler
+
+MB = 1024 * 1024
+FLAGS = flags.FLAGS
+
+
+class FakeHost(object):
+    def __init__(self, host_id, free_ram, io):
+        self.id = host_id
+        self.free_ram = free_ram
+        self.io = io
+
+
+class WeightedSumTestCase(test.TestCase):
+    def test_empty_domain(self):
+        domain = []
+        weighted_fns = []
+        result = least_cost.weighted_sum(domain, weighted_fns)
+        expected = []
+        self.assertEqual(expected, result)
+
+    def test_basic_costing(self):
+        hosts = [
+            FakeHost(1, 512 * MB, 100),
+            FakeHost(2, 256 * MB, 400),
+            FakeHost(3, 512 * MB, 100)
+        ]
+
+        weighted_fns = [
+            (1, lambda h: h.free_ram),  # Fill-first, free_ram is a *cost*
+            (2, lambda h: h.io),  # Avoid high I/O
+        ]
+
+        costs = least_cost.weighted_sum(
+            domain=hosts, weighted_fns=weighted_fns)
+
+        # Each 256 MB unit of free-ram contributes 0.5 points by way of:
+        #   cost = weight * (score/max_score) = 1 * (256/512) = 0.5
+        # Each 100 iops of IO adds 0.5 points by way of:
+        #   cost = 2 * (100/400) = 2 * 0.25 = 0.5
+        expected = [1.5, 2.5, 1.5]
+        self.assertEqual(expected, costs)
+
+
+class LeastCostSchedulerTestCase(test.TestCase):
+    def setUp(self):
+        super(LeastCostSchedulerTestCase, self).setUp()
+
+        class FakeZoneManager:
+            pass
+
+        zone_manager = FakeZoneManager()
+
+        states = test_zone_aware_scheduler.fake_zone_manager_service_states(
+            num_hosts=10)
+        zone_manager.service_states = states
+
+        self.sched = least_cost.LeastCostScheduler()
+        self.sched.zone_manager = zone_manager
+
+    def tearDown(self):
+        super(LeastCostSchedulerTestCase, self).tearDown()
+
+    def assertWeights(self, expected, num, request_spec, hosts):
+        weighted = self.sched.weigh_hosts(num, request_spec, hosts)
+        self.assertDictListMatch(weighted, expected, approx_equal=True)
+
+    def test_no_hosts(self):
+        num = 1
+        request_spec = {}
+        hosts = []
+
+        expected = []
+        self.assertWeights(expected, num, request_spec, hosts)
+
+    def test_noop_cost_fn(self):
+        FLAGS.least_cost_scheduler_cost_functions = [
+            'nova.scheduler.least_cost.noop_cost_fn'
+        ]
+        FLAGS.noop_cost_fn_weight = 1
+
+        num = 1
+        request_spec = {}
+        hosts = self.sched.filter_hosts(num, request_spec)
+
+        expected = [dict(weight=1, hostname=hostname)
+                    for hostname, caps in hosts]
+        self.assertWeights(expected, num, request_spec, hosts)
+
+    def test_cost_fn_weights(self):
+        FLAGS.least_cost_scheduler_cost_functions = [
+            'nova.scheduler.least_cost.noop_cost_fn'
+        ]
+        FLAGS.noop_cost_fn_weight = 2
+
+        num = 1
+        request_spec = {}
+        hosts = self.sched.filter_hosts(num, request_spec)
+
+        expected = [dict(weight=2, hostname=hostname)
+                    for hostname, caps in hosts]
+        self.assertWeights(expected, num, request_spec, hosts)
+
+    def test_fill_first_cost_fn(self):
+        FLAGS.least_cost_scheduler_cost_functions = [
+            'nova.scheduler.least_cost.fill_first_cost_fn'
+        ]
+        FLAGS.fill_first_cost_fn_weight = 1
+
+        num = 1
+        request_spec = {}
+        hosts = self.sched.filter_hosts(num, request_spec)
+
+        expected = []
+        for idx, (hostname, caps) in enumerate(hosts):
+            # Costs are normalized so over 10 hosts, each host with increasing
+            # free ram will cost 1/N more. Since the lowest cost host has some
+            # free ram, we add in the 1/N for the base_cost
+            weight = 0.1 + (0.1 * idx)
+            weight_dict = dict(weight=weight, hostname=hostname)
+            expected.append(weight_dict)
+
+        self.assertWeights(expected, num, request_spec, hosts)
diff --git a/nova/tests/test_scheduler.py b/nova/tests/scheduler/test_scheduler.py
index 54b3f80fb..50b6b52c6 100644
--- a/nova/tests/test_scheduler.py
+++ b/nova/tests/scheduler/test_scheduler.py
@@ -61,7 +61,8 @@ class SchedulerTestCase(test.TestCase):
     """Test case for scheduler"""
     def setUp(self):
         super(SchedulerTestCase, self).setUp()
-        self.flags(scheduler_driver='nova.tests.test_scheduler.TestDriver')
+        driver = 'nova.tests.scheduler.test_scheduler.TestDriver'
+        self.flags(scheduler_driver=driver)
 
     def _create_compute_service(self):
         """Create compute-manager(ComputeNode and Service record)."""
@@ -196,7 +197,7 @@ class ZoneSchedulerTestCase(test.TestCase):
         service.topic = 'compute'
         service.id = kwargs['id']
         service.availability_zone = kwargs['zone']
-        service.created_at = datetime.datetime.utcnow()
+        service.created_at = utils.utcnow()
         return service
 
     def test_with_two_zones(self):
@@ -290,7 +291,7 @@ class SimpleDriverTestCase(test.TestCase):
         dic['host'] = kwargs.get('host', 'dummy')
         s_ref = db.service_create(self.context, dic)
         if 'created_at' in kwargs.keys() or 'updated_at' in kwargs.keys():
-            t = datetime.datetime.utcnow() - datetime.timedelta(0)
+            t = utils.utcnow() - datetime.timedelta(0)
             dic['created_at'] = kwargs.get('created_at', t)
             dic['updated_at'] = kwargs.get('updated_at', t)
             db.service_update(self.context, s_ref['id'], dic)
@@ -401,7 +402,7 @@ class SimpleDriverTestCase(test.TestCase):
                                    FLAGS.compute_manager)
         compute1.start()
         s1 = db.service_get_by_args(self.context, 'host1', 'nova-compute')
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         delta = datetime.timedelta(seconds=FLAGS.service_down_time * 2)
         past = now - delta
         db.service_update(self.context, s1['id'], {'updated_at': past})
@@ -542,7 +543,7 @@ class SimpleDriverTestCase(test.TestCase):
     def test_wont_sechedule_if_specified_host_is_down(self):
         compute1 = self.start_service('compute', host='host1')
         s1 = db.service_get_by_args(self.context, 'host1', 'nova-compute')
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         delta = datetime.timedelta(seconds=FLAGS.service_down_time * 2)
         past = now - delta
         db.service_update(self.context, s1['id'], {'updated_at': past})
@@ -692,7 +693,7 @@ class SimpleDriverTestCase(test.TestCase):
         dic = {'instance_id': instance_id, 'size': 1}
         v_ref = db.volume_create(self.context, {'instance_id': instance_id,
                                                 'size': 1})
-        t1 = datetime.datetime.utcnow() - datetime.timedelta(1)
+        t1 = utils.utcnow() - datetime.timedelta(1)
         dic = {'created_at': t1, 'updated_at': t1, 'binary': 'nova-volume',
                'topic': 'volume', 'report_count': 0}
         s_ref = db.service_create(self.context, dic)
@@ -709,7 +710,7 @@ class SimpleDriverTestCase(test.TestCase):
         """Confirms src-compute node is alive."""
         instance_id = self._create_instance()
         i_ref = db.instance_get(self.context, instance_id)
-        t = datetime.datetime.utcnow() - datetime.timedelta(10)
+        t = utils.utcnow() - datetime.timedelta(10)
         s_ref = self._create_compute_service(created_at=t, updated_at=t,
                                              host=i_ref['host'])
 
@@ -737,7 +738,7 @@ class SimpleDriverTestCase(test.TestCase):
         """Confirms exception raises in case dest host does not exist."""
         instance_id = self._create_instance()
         i_ref = db.instance_get(self.context, instance_id)
-        t = datetime.datetime.utcnow() - datetime.timedelta(10)
+        t = utils.utcnow() - datetime.timedelta(10)
         s_ref = self._create_compute_service(created_at=t, updated_at=t,
                                              host=i_ref['host'])
 
@@ -796,7 +797,7 @@ class SimpleDriverTestCase(test.TestCase):
         # mocks for live_migration_common_check()
         instance_id = self._create_instance()
         i_ref = db.instance_get(self.context, instance_id)
-        t1 = datetime.datetime.utcnow() - datetime.timedelta(10)
+        t1 = utils.utcnow() - datetime.timedelta(10)
         s_ref = self._create_compute_service(created_at=t1, updated_at=t1,
                                              host=dest)
 
diff --git a/nova/tests/test_zone_aware_scheduler.py b/nova/tests/scheduler/test_zone_aware_scheduler.py
index 72b74be20..561fdea94 100644
--- a/nova/tests/test_zone_aware_scheduler.py
+++ b/nova/tests/scheduler/test_zone_aware_scheduler.py
@@ -22,6 +22,37 @@ from nova.scheduler import zone_aware_scheduler
 from nova.scheduler import zone_manager
 
 
+def _host_caps(multiplier):
+    # Returns host capabilities in the following way:
+    # host1 = memory:free 10 (100max)
+    #         disk:available 100 (1000max)
+    # hostN = memory:free 10 + 10N
+    #         disk:available 100 + 100N
+    # in other words: hostN has more resources than host0
+    # which means ... don't go above 10 hosts.
+    return {'host_name-description': 'XenServer %s' % multiplier,
+            'host_hostname': 'xs-%s' % multiplier,
+            'host_memory_total': 100,
+            'host_memory_overhead': 10,
+            'host_memory_free': 10 + multiplier * 10,
+            'host_memory_free-computed': 10 + multiplier * 10,
+            'host_other-config': {},
+            'host_ip_address': '192.168.1.%d' % (100 + multiplier),
+            'host_cpu_info': {},
+            'disk_available': 100 + multiplier * 100,
+            'disk_total': 1000,
+            'disk_used': 0,
+            'host_uuid': 'xxx-%d' % multiplier,
+            'host_name-label': 'xs-%s' % multiplier}
+
+
+def fake_zone_manager_service_states(num_hosts):
+    states = {}
+    for x in xrange(num_hosts):
+        states['host%02d' % (x + 1)] = {'compute': _host_caps(x)}
+    return states
+
+
 class FakeZoneAwareScheduler(zone_aware_scheduler.ZoneAwareScheduler):
     def filter_hosts(self, num, specs):
         # NOTE(sirp): this is returning [(hostname, services)]
diff --git a/nova/tests/test_auth.py b/nova/tests/test_auth.py
index f02dd94b7..7d00bddfe 100644
--- a/nova/tests/test_auth.py
+++ b/nova/tests/test_auth.py
@@ -86,6 +86,7 @@ class _AuthManagerBaseTestCase(test.TestCase):
         super(_AuthManagerBaseTestCase, self).setUp()
         self.flags(connection_type='fake')
         self.manager = manager.AuthManager(new=True)
+        self.manager.mc.cache = {}
 
     def test_create_and_find_user(self):
         with user_generator(self.manager):
diff --git a/nova/tests/test_compute.py b/nova/tests/test_compute.py
index 25454087d..b4ac2dbc4 100644
--- a/nova/tests/test_compute.py
+++ b/nova/tests/test_compute.py
@@ -19,7 +19,6 @@
 Tests For Compute
 """
 
-import datetime
 import mox
 import stubout
 
@@ -217,12 +216,12 @@ class ComputeTestCase(test.TestCase):
         instance_ref = db.instance_get(self.context, instance_id)
         self.assertEqual(instance_ref['launched_at'], None)
         self.assertEqual(instance_ref['deleted_at'], None)
-        launch = datetime.datetime.utcnow()
+        launch = utils.utcnow()
         self.compute.run_instance(self.context, instance_id)
         instance_ref = db.instance_get(self.context, instance_id)
         self.assert_(instance_ref['launched_at'] > launch)
         self.assertEqual(instance_ref['deleted_at'], None)
-        terminate = datetime.datetime.utcnow()
+        terminate = utils.utcnow()
         self.compute.terminate_instance(self.context, instance_id)
         self.context = self.context.elevated(True)
         instance_ref = db.instance_get(self.context, instance_id)
diff --git a/nova/tests/test_console.py b/nova/tests/test_console.py
index 1a9a867ee..831e7670f 100644
--- a/nova/tests/test_console.py
+++ b/nova/tests/test_console.py
@@ -20,8 +20,6 @@
 Tests For Console proxy.
 """
 
-import datetime
-
 from nova import context
 from nova import db
 from nova import exception
diff --git a/nova/tests/test_libvirt.py b/nova/tests/test_libvirt.py
index 687964094..b6b36745a 100644
--- a/nova/tests/test_libvirt.py
+++ b/nova/tests/test_libvirt.py
@@ -724,6 +724,31 @@ class LibvirtConnTestCase(test.TestCase):
         super(LibvirtConnTestCase, self).tearDown()
 
 
+class NWFilterFakes:
+    def __init__(self):
+        self.filters = {}
+
+    def nwfilterLookupByName(self, name):
+        if name in self.filters:
+            return self.filters[name]
+        raise libvirt.libvirtError('Filter Not Found')
+
+    def filterDefineXMLMock(self, xml):
+        class FakeNWFilterInternal:
+            def __init__(self, parent, name):
+                self.name = name
+                self.parent = parent
+
+            def undefine(self):
+                del self.parent.filters[self.name]
+                pass
+        tree = xml_to_tree(xml)
+        name = tree.get('name')
+        if name not in self.filters:
+            self.filters[name] = FakeNWFilterInternal(self, name)
+        return True
+
+
 class IptablesFirewallTestCase(test.TestCase):
     def setUp(self):
         super(IptablesFirewallTestCase, self).setUp()
@@ -741,6 +766,20 @@ class IptablesFirewallTestCase(test.TestCase):
         self.fw = firewall.IptablesFirewallDriver(
                       get_connection=lambda: self.fake_libvirt_connection)
 
+    def lazy_load_library_exists(self):
+        """check if libvirt is available."""
+        # try to connect libvirt. if fail, skip test.
+        try:
+            import libvirt
+            import libxml2
+        except ImportError:
+            return False
+        global libvirt
+        libvirt = __import__('libvirt')
+        connection.libvirt = __import__('libvirt')
+        connection.libxml2 = __import__('libxml2')
+        return True
+
     def tearDown(self):
         self.manager.delete_project(self.project)
         self.manager.delete_user(self.user)
@@ -946,6 +985,40 @@ class IptablesFirewallTestCase(test.TestCase):
         self.mox.ReplayAll()
         self.fw.do_refresh_security_group_rules("fake")
 
+    def test_unfilter_instance_undefines_nwfilter(self):
+        # Skip if non-libvirt environment
+        if not self.lazy_load_library_exists():
+            return
+
+        admin_ctxt = context.get_admin_context()
+
+        fakefilter = NWFilterFakes()
+        self.fw.nwfilter._conn.nwfilterDefineXML =\
+                               fakefilter.filterDefineXMLMock
+        self.fw.nwfilter._conn.nwfilterLookupByName =\
+                               fakefilter.nwfilterLookupByName
+
+        instance_ref = self._create_instance_ref()
+        inst_id = instance_ref['id']
+        instance = db.instance_get(self.context, inst_id)
+
+        ip = '10.11.12.13'
+        network_ref = db.project_get_network(self.context, 'fake')
+        fixed_ip = {'address': ip, 'network_id': network_ref['id']}
+        db.fixed_ip_create(admin_ctxt, fixed_ip)
+        db.fixed_ip_update(admin_ctxt, ip, {'allocated': True,
+                                            'instance_id': inst_id})
+        self.fw.setup_basic_filtering(instance)
+        self.fw.prepare_instance_filter(instance)
+        self.fw.apply_instance_filter(instance)
+        original_filter_count = len(fakefilter.filters)
+        self.fw.unfilter_instance(instance)
+
+        # should undefine just the instance filter
+        self.assertEqual(original_filter_count - len(fakefilter.filters), 1)
+
+        db.instance_destroy(admin_ctxt, instance_ref['id'])
+
 
 class NWFilterTestCase(test.TestCase):
     def setUp(self):
@@ -1122,3 +1195,37 @@ class NWFilterTestCase(test.TestCase):
                                                  network_info,
                                                  "fake")
         self.assertEquals(len(result), 3)
+
+    def test_unfilter_instance_undefines_nwfilters(self):
+        admin_ctxt = context.get_admin_context()
+
+        fakefilter = NWFilterFakes()
+        self.fw._conn.nwfilterDefineXML = fakefilter.filterDefineXMLMock
+        self.fw._conn.nwfilterLookupByName = fakefilter.nwfilterLookupByName
+
+        instance_ref = self._create_instance()
+        inst_id = instance_ref['id']
+
+        self.security_group = self.setup_and_return_security_group()
+
+        db.instance_add_security_group(self.context, inst_id,
+                                       self.security_group.id)
+
+        instance = db.instance_get(self.context, inst_id)
+
+        ip = '10.11.12.13'
+        network_ref = db.project_get_network(self.context, 'fake')
+        fixed_ip = {'address': ip, 'network_id': network_ref['id']}
+        db.fixed_ip_create(admin_ctxt, fixed_ip)
+        db.fixed_ip_update(admin_ctxt, ip, {'allocated': True,
+                                            'instance_id': inst_id})
+        self.fw.setup_basic_filtering(instance)
+        self.fw.prepare_instance_filter(instance)
+        self.fw.apply_instance_filter(instance)
+        original_filter_count = len(fakefilter.filters)
+        self.fw.unfilter_instance(instance)
+
+        # should undefine 2 filters: instance and instance-secgroup
+        self.assertEqual(original_filter_count - len(fakefilter.filters), 2)
+
+        db.instance_destroy(admin_ctxt, instance_ref['id'])
diff --git a/nova/tests/test_middleware.py b/nova/tests/test_middleware.py
index 6564a6955..40d117c45 100644
--- a/nova/tests/test_middleware.py
+++ b/nova/tests/test_middleware.py
@@ -16,7 +16,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import datetime
 import webob
 import webob.dec
 import webob.exc
diff --git a/nova/utils.py b/nova/utils.py
index 4e1b7c26a..e77c80262 100644
--- a/nova/utils.py
+++ b/nova/utils.py
@@ -309,7 +309,7 @@ def  get_my_linklocal(interface):
 
 
 def utcnow():
-    """Overridable version of datetime.datetime.utcnow."""
+    """Overridable version of utils.utcnow."""
     if utcnow.override_time:
         return utcnow.override_time
     return datetime.datetime.utcnow()
diff --git a/nova/virt/libvirt/firewall.py b/nova/virt/libvirt/firewall.py
index 12727f2b1..84153fa1e 100644
--- a/nova/virt/libvirt/firewall.py
+++ b/nova/virt/libvirt/firewall.py
@@ -285,8 +285,29 @@ class NWFilterFirewall(FirewallDriver):
         tpool.execute(self._conn.nwfilterDefineXML, xml)
 
     def unfilter_instance(self, instance):
-        # Nothing to do
-        pass
+        """Clear out the nwfilter rules."""
+        network_info = netutils.get_network_info(instance)
+        instance_name = instance.name
+        for (network, mapping) in network_info:
+            nic_id = mapping['mac'].replace(':', '')
+            instance_filter_name = self._instance_filter_name(instance, nic_id)
+
+            try:
+                self._conn.nwfilterLookupByName(instance_filter_name).\
+                                                    undefine()
+            except libvirt.libvirtError:
+                LOG.debug(_('The nwfilter(%(instance_filter_name)s) '
+                            'for %(instance_name)s is not found.') % locals())
+
+        instance_secgroup_filter_name =\
+            '%s-secgroup' % (self._instance_filter_name(instance))
+
+        try:
+            self._conn.nwfilterLookupByName(instance_secgroup_filter_name)\
+                                            .undefine()
+        except libvirt.libvirtError:
+            LOG.debug(_('The nwfilter(%(instance_secgroup_filter_name)s) '
+                        'for %(instance_name)s is not found.') % locals())
 
     def prepare_instance_filter(self, instance, network_info=None):
         """
@@ -452,6 +473,7 @@ class IptablesFirewallDriver(FirewallDriver):
         if self.instances.pop(instance['id'], None):
             self.remove_filters_for_instance(instance)
             self.iptables.apply()
+            self.nwfilter.unfilter_instance(instance)
         else:
             LOG.info(_('Attempted to unfilter instance %s which is not '
                      'filtered'), instance['id'])
diff --git a/nova/virt/xenapi/fake.py b/nova/virt/xenapi/fake.py
index 5d3b67417..113198689 100644
--- a/nova/virt/xenapi/fake.py
+++ b/nova/virt/xenapi/fake.py
@@ -51,13 +51,13 @@ A fake XenAPI SDK.
 """
 
 
-import datetime
 import uuid
 
 from pprint import pformat
 
 from nova import exception
 from nova import log as logging
+from nova import utils
 
 
 _CLASSES = ['host', 'network', 'session', 'SR', 'VBD',
@@ -536,7 +536,7 @@ class SessionBase(object):
         except Failure, exc:
             task['error_info'] = exc.details
             task['status'] = 'failed'
-        task['finished'] = datetime.datetime.now()
+        task['finished'] = utils.utcnow()
         return task_ref
 
     def _check_session(self, params):
diff --git a/nova/volume/api.py b/nova/volume/api.py
index 5804955f7..b07f2e94b 100644
--- a/nova/volume/api.py
+++ b/nova/volume/api.py
@@ -20,14 +20,13 @@
 Handles all requests relating to volumes.
 """
 
-import datetime
 
-from nova import db
 from nova import exception
 from nova import flags
 from nova import log as logging
 from nova import quota
 from nova import rpc
+from nova import utils
 from nova.db import base
 
 FLAGS = flags.FLAGS
@@ -78,7 +77,7 @@ class API(base.Base):
         volume = self.get(context, volume_id)
         if volume['status'] != "available":
             raise exception.ApiError(_("Volume status must be available"))
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         self.db.volume_update(context, volume_id, {'status': 'deleting',
                                                    'terminated_at': now})
         host = volume['host']
diff --git a/nova/volume/manager.py b/nova/volume/manager.py
index ff53f0701..798bd379a 100644
--- a/nova/volume/manager.py
+++ b/nova/volume/manager.py
@@ -42,8 +42,6 @@ intact.
 
 """
 
-import datetime
-
 
 from nova import context
 from nova import exception
@@ -127,7 +125,7 @@ class VolumeManager(manager.SchedulerDependentManager):
                                   volume_ref['id'], {'status': 'error'})
             raise
 
-        now = datetime.datetime.utcnow()
+        now = utils.utcnow()
         self.db.volume_update(context,
                               volume_ref['id'], {'status': 'available',
                                                  'launched_at': now})
diff --git a/plugins/xenserver/xenapi/etc/xapi.d/plugins/glance b/plugins/xenserver/xenapi/etc/xapi.d/plugins/glance
index 0c00d168b..46031ebe8 100644
--- a/plugins/xenserver/xenapi/etc/xapi.d/plugins/glance
+++ b/plugins/xenserver/xenapi/etc/xapi.d/plugins/glance
@@ -244,7 +244,7 @@ def _upload_tarball(staging_path, image_id, glance_host, glance_port, os_type):
     conn = httplib.HTTPConnection(glance_host, glance_port)
     # NOTE(sirp): httplib under python2.4 won't accept a file-like object
     # to request
-    conn.putrequest('PUT', '/images/%s' % image_id)
+    conn.putrequest('PUT', '/v1/images/%s' % image_id)
 
     # NOTE(sirp): There is some confusion around OVF. Here's a summary of
     # where we currently stand:
diff --git a/tools/pip-requires b/tools/pip-requires
index f1c5b2003..e81ef944a 100644
--- a/tools/pip-requires
+++ b/tools/pip-requires
@@ -33,3 +33,4 @@ suds==0.4
 coverage
 nosexcover
 GitPython
+paramiko